Hi there,
And Welcome here…
So that is one of the Nicer kits on the WebSite, Also is the Link to the WIKI (bottom page) that is probably the most comprehensive GIT of the whole lora corral of products. 
The Battery monitoring has been the achelies heal of the Xiao Series, they need to get with the REAL word and add a PMIC ic to there stuff ASAP! imo. 
HTH
GL 
PJ 